It seems to me that, while most businesses could benefit from using a Business Blog as part of their marketing and business development activities, there are some types of companies which would find them particularly beneficial.

Companies which need to present a human face to their activities:
some professional services organisations have been known to suffer from a bland image. Using a blog, you can break down some of these preconceptions and reveal some of the personalities carrying out the work which will help to engender greater trust in what is a customer focused environment.

Companies which rely on their specialist knowledge to attract clients:
consistently demonstrating expertise in a chosen field can quickly help to build a positive reputation and encourage potential clients to gravitate towards you. Client case studies go part of the way, but displaying both your general and specialised knowledge over a period of time in a Business blog helps more than a sanitised case study can ever do. Think of it as multiple case studies on steroids if you like. This is particularly relevant for independent consultants and specialist consultancies.

Companies which have progressed beyond the hard sell approach:
direct advertising and the hard sell has become less and less successful as an approach. However, an educational marketing approach, where you provide potential clients with information on which to make their own informed decision on their purchase, has gone from strength to strength.

Companies wanting to become more of a partner than a supplier:
as you engage potential clients through your Business Blog, you develop trust and a relationship which can position you as a partner rather than a simple supplier. People prefer to work with and buy from people and companies that they trust and a blog will help to achieve this.

Companies wishing to be THE information resource for their market niche: most of the information that your prospective clients are looking for is available on the web, it is just a case of finding it. So rather than let potential clients find it on a competitors site, provide it yourself or provide links to it on your Blog. You will become the preferred place to go for this type of information and so attract anyone interested in your niche to your blog. This is turn provides you with the ideal opportunity to open a dialogue with them.

Companies organising conferences, seminars and exhibitions:
blogs are the ideal focal point for collating and distributing information to attendees pre-Conference and for gathering feedback from them during and after the Event. You can update the conference details and add new information yourself, and you automatically develop a powerful online Search Engine marketing tool as well.

Companies looking to develop a network or community around themselves:
as a networking tool, a business blog can help in many different ways but one of its most powerful is when it allows the creation of a network of like minded people interested in a particular area. It is particularly positive for the company setting this up and running it because they find themselves at the centre of this network and therefore in a high profile position.

Companies developing new products or services:
customer feedback and input is essential in the product development process. By taking the step to allow this feedback to take place on a Blog, you are allowing discussions and generating ideas which can be invaluable to the process. Added to this, you have a group of people who have contributed to the product and so are likely to be its strongest evangelists and advocates.